UFH between joists, what flooring deck?

[revelation]

Hi all,

 

We are looking to install UFH between joists in our loft conversation and our first floor bedrooms.  We were planning to run our pipes on aluminium spreader plates with insulation directly below them between the joists.

 

I would like some advice on what is the best deck to put on top of the joists.  The builders don't have any experience with UFH thats not in screed and have normally put caber-deck and then the final flooring when they have done normal (non UFH) floors.   We have 18mm engineered tongue and groove wood flooring as our final floor finish.  We would like a solution which is going to give the best\fastest heating up times.

 

Thank you in advance.

[PeterW]

Just use Caber/Egger and that will be fine. Depending on joist spacing, 18mm or 22mm will be needed. Just get them to glue it to the joists and make sure if they nail it down they avoid the pipes where it crosses the joists. 

[Temp]

Have you purchased the 18mm engineered wood flooring yet? If not then 21mm can go direct onto the joists. 

[revelation]

On 04/10/2020 at 00:28, PeterW said:

Just use Caber/Egger and that will be fine. Depending on joist spacing, 18mm or 22mm will be needed. Just get them to glue it to the joists and make sure if they nail it down they avoid the pipes where it crosses the joists. 

 

Our joist spacing is either 300mm or 400mm on 75mm wide joist.  So if we were going down the Caber/Egger route we would be going for 18mm and then the engineered flooring on top of that.

 

From your experience will caber/egger allow for decent heat up times? Is there product that will work better for underfloor heating?

 

Regards

[revelation]

On 04/10/2020 at 04:26, Temp said:

Have you purchased the 18mm engineered wood flooring yet? If not then 21mm can go direct onto the joists. 

 

Unfortunately I have already bought the 18mm engineered wood floor, I managed to get some walnut at a really good price last year.  I didn't really think about this process at the time.  My builders had said the 18mm could go straight onto the joists, but were concerned about where the joists may meet in the space between the joists.  In most places we do have 300mm centres, we want the floors to feel really solid so unless its certain that it will work we are inclined to put something else down first then the flooring ontop.

 

[Temp]

Others may disagree but I would have a rethink. If you put down 18mm osb then 18mm engineered Wood you end up with 36mm overall. We have 21mm in a house built to Building regs standards as they were in 2005-7. We have found we need quite high flow temperatures to push enough heat into the rooms. In addition the return temperatures can be quite high sometimes. There are other threads on here where I suspect having too much wood above the ufh might be the reason they are seeing long warm up times.

 

 

[revelation]

9 hours ago, Temp said:

Others may disagree but I would have a rethink. If you put down 18mm osb then 18mm engineered Wood you end up with 36mm overall. We have 21mm in a house built to Building regs standards as they were in 2005-7. We have found we need quite high flow temperatures to push enough heat into the rooms. In addition the return temperatures can be quite high sometimes. There are other threads on here where I suspect having too much wood above the ufh might be the reason they are seeing long warm up times.

 

 

 

I am worried about long warm up times, do you have insulation directly under your pipes?  

 

Worst case scenario I would consider getting 21mm, ideally I would like to utilise what I have if it will work well with some kind of thinner deck board below.

[PeterW]

19 hours ago, revelation said:

 

Unfortunately I have already bought the 18mm engineered wood floor, I managed to get some walnut at a really good price last year.  I didn't really think about this process at the time.  My builders had said the 18mm could go straight onto the joists, but were concerned about where the joists may meet in the space between the joists.  In most places we do have 300mm centres, we want the floors to feel really solid so unless its certain that it will work we are inclined to put something else down first then the flooring ontop.

 

18mm over 300 centres will be ok as a structural floor as long as it is long planks spanning at least 3 joists. Your issue will be that it is not the “correct” floor type and you cannot get the spans so you will need to use a minimum 18mm construction floor such as OSB or Ply before you add the wood floor on top. 

[Temp]

12 hours ago, revelation said:

 

I am worried about long warm up times, do you have insulation directly under your pipes?  

 

Yes we have about 80mm of PIR then beam and block floor. If building again I would go for much more.

[revelation]

On 08/10/2020 at 08:00, PeterW said:

18mm over 300 centres will be ok as a structural floor as long as it is long planks spanning at least 3 joists. Your issue will be that it is not the “correct” floor type and you cannot get the spans so you will need to use a minimum 18mm construction floor such as OSB or Ply before you add the wood floor on top. 

 

Would the 18mm caber before the engineered floor add much time to warm up?

 

Another issue that has come to mind if we went for the floor direct onto the joists would be where we have bathrooms that we plan to tile, they will need some kind of deck under so if we had to put 18mm caber and then maybe a decoupling membrane and then tiles we could end up with a bit of difference in the floor levels.

[revelation]

21 hours ago, Temp said:

 

Yes we have about 80mm of PIR then beam and block floor. If building again I would go for much more.

 

I am starting to lean towards putting it directly onto the joists.  On the ground floor our UFH will be in screed with at least 100mm of insulation below which will work fine.   I am looking to put about 50mm of kingpin between the joists of the GF/1st Floor and 1st Floor/2nd Floor.

[PeterW]

43 minutes ago, revelation said:

 

I am starting to lean towards putting it directly onto the joists.  On the ground floor our UFH will be in screed with at least 100mm of insulation below which will work fine.   I am looking to put about 50mm of kingpin between the joists of the GF/1st Floor and 1st Floor/2nd Floor.

 

I would look at a two layer approach to insulation here. First layer against the bottom of the spreader plates using 100mm of rockwool based product  held in place with 50mm of tightly fitted PIR. This will both have an acoustic and heat insulation benefit and also allow the insulation to mould around the pipework and push it tight to the bottom of the flooring.

 

I wouldn't lay the floor direct onto the joists - your plasterers and other trades will damage it, and no amount of protection will help so I would go with an 18mm Caber deck as a working deck and then bond the engineered wood to the caberdeck.

[Nickfromwales]

This will have adverse warm up times regardless of the approach, but no UFH has a very quick warm up time TBH other than UTH ( under tile heating ) over insulated backer boards. I think I would still employ a structural deck first in any instance and I have done similar, many times on previous projects with 1st floor rooms over pozi-joists. The build up was;

• Posi joists at 400mm c's
• UFH spreader plates with 16x2 pipes, 2 pipe runs run void
• 22mm P5 2400x600 T&G deck board, D4 glued and screwed minimum 5 fixings per 600mm joist > board contact area
• 6mm plywood, PVA glue combed with a 3mm tile adhesive trowel for 100% bonded coverage, and also screwed at 120mm c's with 25x8mm screws
• Tile adhesive and porcelain tiles.

Only complaint I had from the client was "how do you turn it down?"  

 

You're already at the upper-most part of the heated envelope so I doubt that space will need much in terms of additional heat input ( unless it's an old / poorly insulted and draughty building? ) when the heating on other floors are likely to also be running, so my approach would be to fit plywood baffles with the upper-most surface 115mm below the top of the joists. If following B-Reg's ( or not ) you may well have to install acoustic insulation batts to stop foot traffic / other noise from emitting downwards, so use that to kill 2 birds. I'd sit the 100mm batts on top of the plywood baffles which would leave a ~15mm gap at the top ( between the top of the batts and the top of the joists ). The spreader plates would then sit atop the batts and be slightly proud / distended upwards due to the plates being 2mm > 16mm > 2mm so ~20mm overall thus setting the plate upper surface ~5mm above the joist top level. Gluing and screwing the deck boards down will force the plates into the insulation and maintain surface contact between the plates and the deck boards, which is critical for anything resembling good heat transfer from water > plate > deck > room. I always screw and never nail, and after 23 years plus with zero complaints of "squeaky floors" I will be continuing to do so.

 

You will need higher flow temps in the upper levels, vs the ground floor for eg, so you must make sure that for each discipline you have a manifold and blending set to suit ( so you can define the different flow temps to suit each floor ). Some will fit a manifold on the 1st floor and then run pipes down to the ground floor if GF space is at a premium, but that will not work for sharing the same flow temp between the ground and 1st floor from a single larger manifold, so a manifold per floor is the benchmark so you can adjust / fine-tune these flow temps, per floor, to suit.

[revelation]

On 11/10/2020 at 12:04, Nickfromwales said:

This will have adverse warm up times regardless of the approach, but no UFH has a very quick warm up time TBH other than UTH ( under tile heating ) over insulated backer boards. I think I would still employ a structural deck first in any instance and I have done similar, many times on previous projects with 1st floor rooms over pozi-joists. The build up was;

• Posi joists at 400mm c's
• UFH spreader plates with 16x2 pipes, 2 pipe runs run void
• 22mm P5 2400x600 T&G deck board, D4 glued and screwed minimum 5 fixings per 600mm joist > board contact area
• 6mm plywood, PVA glue combed with a 3mm tile adhesive trowel for 100% bonded coverage, and also screwed at 120mm c's with 25x8mm screws
• Tile adhesive and porcelain tiles.

Only complaint I had from the client was "how do you turn it down?"  

 

You're already at the upper-most part of the heated envelope so I doubt that space will need much in terms of additional heat input ( unless it's an old / poorly insulted and draughty building? ) when the heating on other floors are likely to also be running, so my approach would be to fit plywood baffles with the upper-most surface 115mm below the top of the joists. If following B-Reg's ( or not ) you may well have to install acoustic insulation batts to stop foot traffic / other noise from emitting downwards, so use that to kill 2 birds. I'd sit the 100mm batts on top of the plywood baffles which would leave a ~15mm gap at the top ( between the top of the batts and the top of the joists ). The spreader plates would then sit atop the batts and be slightly proud / distended upwards due to the plates being 2mm > 16mm > 2mm so ~20mm overall thus setting the plate upper surface ~5mm above the joist top level. Gluing and screwing the deck boards down will force the plates into the insulation and maintain surface contact between the plates and the deck boards, which is critical for anything resembling good heat transfer from water > plate > deck > room. I always screw and never nail, and after 23 years plus with zero complaints of "squeaky floors" I will be continuing to do so.

 

You will need higher flow temps in the upper levels, vs the ground floor for eg, so you must make sure that for each discipline you have a manifold and blending set to suit ( so you can define the different flow temps to suit each floor ). Some will fit a manifold on the 1st floor and then run pipes down to the ground floor if GF space is at a premium, but that will not work for sharing the same flow temp between the ground and 1st floor from a single larger manifold, so a manifold per floor is the benchmark so you can adjust / fine-tune these flow temps, per floor, to suit.

 

Thank you for that.  It was very comprehensive.  We will have a different manifold for the downstairs and the 1st floor/loft.

 

Would 18mm Caber suffice as I am having 18mm wood on top? and in most of the areas I have 300mm joist spacing.  

 

I was planning on using PIR between the joists directly under the spreader plates, would that work well instead of the batts?

 

 

 

 

 

 

 

[Nickfromwales]

5 hours ago, revelation said:

Thank you for that.  It was very comprehensive.  We will have a different manifold for the downstairs and the 1st floor/loft.

 

Would 18mm Caber suffice as I am having 18mm wood on top? and in most of the areas I have 300mm joist spacing.  

 

I was planning on using PIR between the joists directly under the spreader plates, would that work well instead of the batts?

At 300 c’s 18mm will be ample. ?

 

Pointless using PIR as you don’t need the elevated insulation quality, but worse still is it is pretty much acoustically transparent. If it was my house, it would be acoustic batts. Also, the PIR is a pig to work with by comparison, and the dust from cutting it is horrific in closed spaces. 

[revelation]

6 hours ago, Nickfromwales said:

At 300 c’s 18mm will be ample. ?

 

Pointless using PIR as you don’t need the elevated insulation quality, but worse still is it is pretty much acoustically transparent. If it was my house, it would be acoustic batts. Also, the PIR is a pig to work with by comparison, and the dust from cutting it is horrific in closed spaces. 

 

Have I got my understanding of insulating wrong?  I was under the impression that having some kingpan phenolic insulation below (about 50mm, we have a lot left over that were used in other places) would help make sure that all the would be directed above.  I thought about using a standard rockwool too, but not the acoustic.   

 

Is the performance of acoustic rockwool in terms of sound reduction and heat insulation worth while compared to the heat insulation that the kingspanboards would give?

 

[Nickfromwales]

8 minutes ago, revelation said:

 

Is the performance of acoustic rockwool in terms of sound reduction and heat insulation worth while compared to the heat insulation that the kingspanboards would give?

Completely negligible. You just don’t need the higher performing thermal quality of the PIR, but you certainly WILL need the acoustic quality of the acoustic rock wool. The rock wool ( at 100mm ( not 50mm as the PIR would be )) will have more than ample thermal insulation for this upper floor.

Not sure what others would add, but maybe a foil on top of the plywood baffles would ‘reflect’ any downward heat back up. I’ll get my tin hat ready......

[revelation]

7 hours ago, Nickfromwales said:

Completely negligible. You just don’t need the higher performing thermal quality of the PIR, but you certainly WILL need the acoustic quality of the acoustic rock wool. The rock wool ( at 100mm ( not 50mm as the PIR would be )) will have more than ample thermal insulation for this upper floor.

Not sure what others would add, but maybe a foil on top of the plywood baffles would ‘reflect’ any downward heat back up. I’ll get my tin hat ready......

 

instead of the baffles, maybe to utilise the 50mm kingspan I could batten the sides of the joists put the 50mm kingspan board down and then use 50mm of acoustic Rockwool on top?   (As you can tell I'm keen to make full use of any left over materials that I have rather than lose out)

[revelation]

On 09/10/2020 at 13:22, PeterW said:

 

I would look at a two layer approach to insulation here. First layer against the bottom of the spreader plates using 100mm of rockwool based product  held in place with 50mm of tightly fitted PIR. This will both have an acoustic and heat insulation benefit and also allow the insulation to mould around the pipework and push it tight to the bottom of the flooring.

 

I wouldn't lay the floor direct onto the joists - your plasterers and other trades will damage it, and no amount of protection will help so I would go with an 18mm Caber deck as a working deck and then bond the engineered wood to the caberdeck.

 

I think I have settled on the 18mm caber and then the finished flooring ontop.  In the joists I am thinking 50mm Kingspan (K12) and 50mm acoustic Rockwool, a few people have recommended acoustic, i didn't realise that it was so useful.

[Nickfromwales]

2 hours ago, revelation said:

instead of the baffles, maybe to utilise the 50mm kingspan

2 heads always better than one   The only thing I don't like about that idea is that you beat me to it.

Indeed, a plan is hatched........but still bloody 'orrible stuff to cut lol. 

On 09/10/2020 at 13:22, PeterW said:

I would look at a two layer approach to insulation here. First layer against the bottom of the spreader plates using 100mm of rockwool based product  held in place with 50mm of tightly fitted PIR. This will both have an acoustic and heat insulation benefit and also allow the insulation to mould around the pipework and push it tight to the bottom of the flooring.

Credits to the original author   I'll get him next time......

[Deepandy]

On 13/10/2020 at 23:22, revelation said:

 

I think I have settled on the 18mm caber and then the finished flooring ontop.  In the joists I am thinking 50mm Kingspan (K12) and 50mm acoustic Rockwool, a few people have recommended acoustic, i didn't realise that it was so useful.

Revelation, Can you update on the project? I'm about to get going with something very similar and have the same questions/concerns as you had.